1. Field of the Invention
The present invention relates to a light generator suitable to a pumping light generator adapted to generate pumping light for signal amplification, an optical amplifier including the light generator, a control method using the optical amplifier, and an optical communication system including the optical amplification medium.
2. Related Background Art
An optical communication system transmits signal light through an optical fiber transmission line to implement large-capacity high-speed transmission of information. In this optical communication system, the signal light suffers loss during propagation through the optical fiber transmission line, and an optical amplifier for amplifying the signal light is used in order to compensate for the loss. The known optical amplifiers for this purpose include rare-earth-doped optical fiber amplifiers using an optical fiber doped with a rare earth element (e.g., Er), as an optical amplification medium, and Raman amplifiers making use of the stimulated Raman scattering phenomenon in the optical amplification medium. Among them, the Raman amplifiers are recently drawing attention, because they are effective to improvement in noise characteristics and the nonlinear optical phenomena of the optical communication system.
A Raman amplifier of this type is described, for example, in Document 1 “S. Kado, et al., “Broadband flat-noise Raman amplifier using low-noise bi-directionally pumping sources,” ECOC'2001, Postdeadline papers, pp. 38-39 (2001).” In the Raman amplifier 1 described in this Document 1, the optical fiber as an optical amplification medium receives supply of 3-channel pumping light propagating in the same direction as the propagating direction of signal light and 5-channel pumping light propagating in the direction opposite to the propagating direction of the signal light. This supply of the pumping light of multiple channels into the optical amplification medium broadens and flattens a gain spectrum of amplification of signal light in the optical amplification medium. The optical amplifier with the broadband gain spectrum can be suitably applicable to a WDM (Wavelength Division Multiplexing) optical communication system for transmitting multiplexed signal light of multiple channels.